2. Progress on new electron cloud monitors in the PS Christina Yin Vallgren, TE-VSC P. Chiggiato, S. Gilardoni, J. A. Ferreira Somoza G. Iadarola, H. Neupert, G. Sterbini, M. Taborelli Christina Yin Vallgren, PS-LIU meeting 61 17/09/2013

3. Outline 1.Introduction 2.Detailed Summary on Electron-Photon-Emission Experiments in the lab 3.Conclusion: what to do in the PS? 4.Outlook

4. Introduction: Electron cloud build-up in the PS  Measurements of electron cloud in a real magnet, will provide: 1. Prediction of the EC build-up distribution in the PS magnets for higher intensity beams in the frame of the upgrade program. 2. Validation of the EC simulation models and codes.  Two proposals to measure electron cloud in a main magnet 1. Shielded Pick-up 2. Electron-Photon Emission  Earlier discussions: 1. LIU-PS meeting 48 2. LIU-PS meeting 51 3. LIU-PS meeting 59

5. Introduction: Implementation in the PS MU98 [By Teddy Capelli EN/MME] DN63 : optical window DN63 : optical window DN35 : shield pick-up DN35 : shield pick-up

6. Explanation of mechanism of photon emission Direct photoemission PE Inverse photoemission IPE E(e- )< 100eV In our case: E(e- ) = 100 – 1000 eV 1. Primary electrons (PE) of 300eV 2. Generation of secondary electrons (SE) with different energies 3. SE fall into unoccupied states => Light is generated.

7. Progress: Electron-Photon Emission Experiments in the lab 1. Electron gun with BaO cathode Low light emitter (1150K) 3. Sample Bias of +18V 4. Quartz window 5. Collimating lens 6. Optical fiber 7. Andor Shamrock Spectrograph Computer 7. Andor iDus spectroscopy camera 200-770nm 20 o 1.Electron gun: low temperature BaO cathode (1150K) 2.Grid and deflection: prevent the electrons arrive on the sample. 3.Sample: +18 V 4.Quartz window: 200-2000nm transmission 100% 5.Collimating lens: optimized for 200-2500nm 6.Optical fiber: transfer the light from the system to the spectrometer 7.Andor Spectrograph with CCD camera (200-770nm) 2. Grid 2. Deflection 2. Collector

8. Detailed measurement results - Dark current in the system  The CCD detector is cooled using a thermoelectric (TE) cooler to -60 o C to decrease dark current.  The dark background of the detection system is 10-15 counts/s  A slight background signal in the system observed in the red-IR range

9. Detailed measurement results - Dark current in the system  The system is not ideally screened. => Light changes outside chamber can be detected by the CCD  Light off: room window shutter closed, lights off in the lab => dark in the lab.  Light on: room window shutter open.

10. Detailed measurement results  Environment (lights) changes the background, but only above 700 nm  The investigated range in interest should not be influenced.

11. Detailed measurement results  Electron gun on: black body radiation. Light emitted from the filament.  Low temperature BaO cathode => significant increase of photons focus above 600nm due to heating of cathode. System dark current as shown earlier Measured current landing on the sample: I_sample = 2µA per 2 mm2. Grid off: beam on the sample Grid on: beam stopped in the gun This part will not be present in the PS.

12. Detailed measurement results - Photons detected on Cu sample  Energy of electron beam = 300 eV.  Electron current density on Cu sample is 1uA/mm2.  Averaging 10 measurements of 60s integration time with 5 accumulations.  Accumulations to prevent cosmic rays. Accumulation must be performed due to cosmic ray removal option (Cosmic rays can pass through the CCD and produce photoelectrons in a very small area due to the low read noise of the CCD. Therefore each scan will be compared with the previous one, for the presence of unusual feature) 1.Signal: Gun on with beam 2.Background with grid on 3.Background with deflected beam on the collector, not on the sample 4.Background taken without sample (beam impinging far away on the vacuum chamber) It means that the sample surface reflects some photons from the gun filament

13. Detailed measurement results - Photons detected on Cu sample  Which one is the correct background? The result is different if we use the one with grid on (beam blocked in the gun) or the one with the beam deflected in the collector. Data needs to be corrected with sensitivity factors of the grating and the CCD camera

14. Detailed measurement results - Photons detected on Cu sample 60sx5, I_sample = 2uA/2mms60sx5, I_sample = 8uA/2mms The photon counts are proportional to the electron current on the sample

15. Detailed measurement results - Photons detected on Cu sample Efficiency for grating of 150l/mm of 500 nm blaze Quantum efficiency of CCD  Efficiency coefficients: used for correction of measured data.  Grating: 150 l/mm of 500 nm blaze.  CCD: iDus with open electrode (OE) Best option (2000chf) Best option (24000chf)

16. Detailed measurement results - Photons detected on Cu sample 60s x 5, background of grid on 60s x 5, background of deflected beam 100s x 5, background of grid on 200s x 5, background of grid on  Measurement data is reproducible  Proportional to the integration time and sample current  So this is the real signal!

17. Detailed measurement results - Photons detected on Cu sample  Compare with reference  Expected radiation yield from one of the references: 10 -9 – 10 -11 photons/electron  Our measured radiation yield: 10 -11 photons/electron (no optimized system)  We don’t have the peak at the same wavelength. Needs more investigation  Ordered a grating with 70% efficiency for NUV photons  Main peak at 320nm  Polycrystalline Cu  Main peak at 420nm

18. Estimation in the PS Electron density = 1uA/mm2 per turn 60mm 160mm  Assume? that we have a very smart way to collect the photons both on the top and bottom of the chamber with two/several lenses. (feasible or not?)  Maximum of collected area = 2 x 1.25x10 3 mm2  # of electrons = 2 x 1.25x10 3 mm2 x 1e-6C/s mm2 / 1.6e-19C = 1.57x10 16 electrons/s  Assume the radiation yield is about 10 -11 photons/electron, similar solid angle as in the lab system.  # of photons = 1.57x10 5 photons/s  During the 40-50ms electron cloud development of the PS =>  7x10 3 photons in best case

19. Conclusion and summary in the PS  Shall we continue or not?  If we continue, measure the spectrum and estimate radiation yield of stainless steel => should not be any big difference  Due to the low radiation yield, a lot of work is expected in the PS to maximize the photon detection.

20. Outlook - focus on electorn-photon-emission If we continue: 1.Experimental set-up in the lab 1. Upgrade the spectrometer with Grating optimized for NUV range. 2. Upgrade the spectrometer with CCD optimized for NUV range. 2.Experimental set-up in the PS magnet 1. Detector I.Alt 1: Hamamatsu PMT against high magnetic field and high radiation II.Alt 2: iDus DV420A-BU back illuminated CCD with AR coating in the UV region 2. Window or filters I.Alt 1: Quartz (SiO2 200-2000nm ~100%) window or other alternative + shortpass filter (200-500nm 90%) II.Alt 2: Fused Silica UV grade (SiO2): 200-400nm 90% 3. Collimating lens (how many ?) or optical lenses 4. Optical fibers

21. THANK YOU FOR YOUR ATTENTION!